What are the specific functions of a cell membrane?
- import/export specific molecules
- regulate interactions between cells
- regulate interactions between cells and their environment
- transfer info from outside of the cell to inside
- in charge of its movement, shape and growth
What is a cell membrane made up of? What are they held together by?
Lipids and proteins held together by non-covalent interactions
What are the three main types (+) of membrane lipid molecules?
Glycerophospholipids, sphingolipids and sterols (+ glycolipids)
What are the parts of a glycerophospholipid molecule like phosphatidylcholine
A glycerol with 3 linking sites. 2 of them are to fatty acid residues and the 1 is to a phosphate linked to another organic substance like choline
What are the 4 phospholipids in mammalian plasma membranes?
Phosphatidyethanolamine, phosphatidyserine (-), phosphatidylcholine, and sphingomyelin with sphingosine and the basic building block
What is the structure of a sterol? Give an example of a sterol.
Smaller than the others, with ring like structures, a single polar hydroxyl group and variable side chains. Cholesterol!
Phospholipids _____ self-assemble
spontaneously. It's favorable because it minimizes water interactions with the hydrophobic tails of the lipids
What are the consequences of sealed compartments being energetically favored?
If damaged, they will quickly try their best to reseal and polar molecules cannot pass through the lipid bilayer freely
What is a phase transition?
The temperature at which a bi-layer changes from liquid state to a rigid crystalline state (basically a range). Temp phase transition down = membrane fluidity up
Why does a membrane have to be fluid?
To ensure they can efficiently regulate and maintain enzyme activities and transport proteins
How do hydrocarbon tail lengths and cis double bonds affect fluidity?
The shorter the tail, the more fluid. This is due to the reduced interactions and more kinks prevent the membrane from packing tightly together
Cholesterol decreases the _______ of the membrane
fluidity
Wat are glycolipids?
A carbohydrate linked to a polar head group providing great diversity. Attached to the external side of the plasma membrane. Plays a role in cell recognition and adhesion to one another
The lipid bilayer is an _______ structure
A) Symmetric
B) Asymmetric
B) Asymmetric
- Each leaflet has its own composition of lipids and proteins
Cholesterol is distributed _______ in both leaflets
A) Equally
B) Unequally
A) Equally
Explain the 2 types of examples using PI (phosphotidylinositol) as a signaling molecule
Type 1: The extracellular signal causes the cell to activate a relay signal within the cell
Type 2: The extracellular signal causes the cell to send a signaling lipid fragment into the cell
Explain how cell recognition plays an important role in cell death.
Once a cell dies, phosphotidylserine (- charge) that was once inside the cell relocates to the external leaflet . The phosphotidylserine stimulates/attracts the macrophages to engulf and digest the dead cell it is attached to.
What part of the cell is the site of lipid synthesis?
The cytosolic leaflet of the endoplasmic reticulum sends new lipids to the plasma membrane through vesicles
Proteins make up _______% of the membrane mass
25-75%
Draw a fluid mosaic model
A lipid bilayer with hydrophobic tails, hydrophilic heads and scattered proteins embedded or on top of the bilayer
What is the freeze fracture EM?
Where they freeze cells in liquid nitrogen then fracture it with a knife then study it under a microscope
Membrane proteins are typically ______
a) Hydrophobic
b) Hydrophilic
c) Amphiphilic
c) amphiphillic
How are membrane proteins associated with the lipid bilayer?
- Transmembrane proteins (fully embedded in the bilayer)
- Alpha helixes (partially embedded in the cytosolic leaflet)
- Covalently attached to lipid chains (not directly embedded but connected to something else that is)
- Membrane associated (binded to a transmembrane protein)
What are the 3 types of lipid anchors?
- Myristoylation (myristic acid connect to the N terminus)]
- Palmitoylation (palmitic group connect to a cysteine side chain)
- Prenylation (phrenyl group connect to a cysteine side chain)
Multi-pass membrane proteins are shaped in _____ and can be predicted using _____
Alpha helix shaped and can be predicted using its amino acid sequence
What are beta barrels in the membrane?
B sheet strands that form the shape of an empty barrel and are hydrophilic allowing passage of small molecule and hydrophobic in the areas that bind to the interior of the lipid bilayer
Proteins are coated with a ______ layer
carbohydrate
Rates of membrane movement can be measured by FRAP method. What is the FRAP method?
Fluorescent dyes are attached to membrane lipids/proteins and then a portion is bleached. Then the recovery rate is monitored
Go over regulation of protein movement within membranes
slide 40
Protein are restricted to a certain domain by ______
The antibodies on the surface of the cells
T/F membrane proteins can deform/bend lipid bilayers
True
What are lipid rafts
Regions in the membrane that are enriched in sphingolipids, cholesterol, and proteins. Purpose to help proteins with their designated function or transport